1. Field
The present invention relates to a microphone containing a micro-electromechanical system acoustic transducer within the housing of the microphone.
2. Related Art
Microphones containing micro-electromechanical system (MEMS) acoustic transducers (MEMS chips) inside the housing are provided as small form factor microphones (referred to as MEMS mics below). MEMS chips are manufactured using MEMS technology.
First, a typical MEMS mic configuration is described using FIG. 1A, and FIG. 1B. Note, the MEMS mic illustrated in FIG. 1A (refer to U.S. Pat. No. 6,781,231 for example), and the MEMS mic illustrated in FIG. 1B are top-port and bottom-port MEMS mics respectively.
As illustrated in FIG. 1A and FIG. 1B, a typical MEMS mic includes a substrate 31, a cover 32, a housing 30 constituted by the substrate 31 and the cover 32, a MEMS chip 40 (MEMS acoustic transducer), and an Application Specific Integrated Circuit (ASIC) 45. The MEMS chip 40 and the ASIC 45 are arranged side by side on the substrate 31 in the housing 30.
The MEMS chip 40 is an acoustic transducer (condenser microphone) manufactured using MEMS technology. The ASIC 45 is an integrated circuit that amplifies the output of the MEMS chip. In other words the ASIC 45 applies a direct-current voltage between the fixed electrode and the movable electrode of the MEMS chip, and outputs a change in voltage proportional to the resultant change in the capacitance of the MEMS chip.
As illustrated in FIG. 1A and FIG. 1B, usually the MEMS chip 40 is arranged on the substrate 31 so that the center line of the sound port 35 formed in the cover 32 or the substrate 31 passes substantially through the center of the diaphragm 41.
The upper surface of the substrate 31, and the inner surface of the cover 32 are lined with conductive layers 33, 34 that act as an electromagnetic shield to ensure that the microphone is resistant to electromagnetic noise. A plurality of electrodes is provided on the upper surface of the substrate 31 for connection to the plurality of electrodes (electrode pads, and terminals) on the ASIC 45. Additionally, a plurality of electrodes is provided on the under surface of the substrate, electrically connected to the electrodes on the upper surface of the substrate 31.
As further illustrated in FIG. 1A and FIG. 1B, in the typical MEMS mic, the MEMS chip 40 and ASIC 45, and the ASIC 45 and the electrodes on the upper surface of the substrate 31 are connected by wires.
In the types of MEMS mics illustrated in FIG. 1A and FIG. 1B, the space unconnected to the sound port 35 inside the housing 30 is called the back chamber. If the back chamber is narrow as schematically illustrated in FIG. 2, the air within the back chamber acts as an air spring applying a relatively large force to the diaphragm 41, which inhibits the diaphragm 41 from vibrating. If the diaphragm 41 is inhibited in vibrating, the sensitivity of the MEMS mic deteriorates. Consequently, it may be beneficial for the MEMS mic to have a large back chamber.
Furthermore, various types of MEMS mics having configurations different from the configurations illustrated in FIG. 1A and FIG. 1B have been proposed to provide a desired smaller MEMS mic.
For instance, U.S. Pat. No. 7,242,089 proposes to increase the size of the back chamber by creating a cavity 31a within the substrate 31 that functions as a back chamber as illustrated in FIG. 3.
As illustrated in FIG. 4, Japanese Registered Patent Number 5029727 further proposes providing the ASIC 45 near the substrate 31 and providing the MEMS chip 40 near the cover 32 in which the sound port 35 is formed. Finally, as illustrated in FIG. 5, Japanese Registered Patent Number 4947191 proposes providing an ASIC 45′ with an opening, and overlapping the ASIC 45′ and the MEMS chip 40 with the sound port 35.